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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 13] 13.3 Send (only) Standard Error Down a Pipe </TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly & Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1998-08-04T21:36:41Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-260-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch13_01.htm"TITLE="13. Redirecting Input and Output"><LINKREL="prev"HREF="ch13_02.htm"TITLE="13.2 One Argument with a cat Isn't Enough "><LINKREL="next"HREF="ch13_04.htm"TITLE="13.4 Problems Piping to a Pager "></HEAD><BODYBGCOLOR="#FFFFFF"TEXT="#000000"><DIVCLASS="htmlnav"><H1><IMGSRC="gifs/smbanner.gif"ALT="UNIX Power Tools"USEMAP="#srchmap"BORDER="0"></H1><MAPNAME="srchmap"><AREASHAPE="RECT"COORDS="0,0,466,58"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="467,0,514,18"HREF="jobjects/fsearch.htm"ALT="Search this book"></MAP><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch13_02.htm"TITLE="13.2 One Argument with a cat Isn't Enough "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 13.2 One Argument with a cat Isn't Enough "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 13<BR>Redirecting Input and Output</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch13_04.htm"TITLE="13.4 Problems Piping to a Pager "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 13.4 Problems Piping to a Pager "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-0233">13.3 Send (only) Standard Error Down a Pipe </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-14177"></A><ACLASS="indexterm"NAME="AUTOID-14179"></A><ACLASS="indexterm"NAME="AUTOID-14183"></A>A vertical bar character (<CODECLASS="literal">|</CODE>) on a command linepipes the standard output of a process to another process.How can you pipe the standard error, not the standard output?You might want to put a long-running <EMCLASS="emphasis">cruncher</EM> command in the background,save the output to a file, and mail yourself a copy of the errors.In the C shell, run the command in a<SPANCLASS="link">subshell (<ACLASS="linkend"HREF="ch13_07.htm"TITLE="The () Subshell Operators ">13.7</A>)</SPAN>.The standard output of the command is redirected inside the subshell.All that's left outside the subshell is thestandard error; the<ACLASS="indexterm"NAME="AUTOID-14189"></A><SPANCLASS="link"><CODECLASS="literal">|&</CODE> operator (<ACLASS="linkend"HREF="ch13_05.htm"TITLE="Redirection in C Shell: Capture Errors, Too? ">13.5</A>)</SPAN>redirects it (along with the empty standard output) to the<SPANCLASS="link"><EMCLASS="emphasis">mail</EM> (<ACLASS="linkend"HREF="ch01_33.htm"TITLE="UNIX Networking and Communications ">1.33</A>)</SPAN>program:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>(cruncher > </B></CODE><CODECLASS="replaceable"><I>outputfile</I></CODE><CODECLASS="userinput"><B>) |& mail </B></CODE><CODECLASS="replaceable"><I>yourname</I></CODE> &[1] 12345</PRE></BLOCKQUOTE></P><PCLASS="para">Of course, you don't need to put that job<SPANCLASS="link">in the background (<ACLASS="linkend"HREF="ch01_26.htm"TITLE="What a Multiuser System Can Do for You ">1.26</A>)</SPAN>.If you want the standard output to go to your terminal instead of a textfile, use<ACLASS="indexterm"NAME="AUTOID-14204"></A><SPANCLASS="link"><EMCLASS="emphasis">/dev/tty</EM> (<ACLASS="linkend"HREF="ch45_20.htm"TITLE="Overview: Open Files and File Descriptors ">45.20</A>)</SPAN>as the <CODECLASS="replaceable"><I>outputfile</I></CODE>.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-14211"></A>The Bourne shell gives you a lot more flexibility and lets you dojust what you need.The disadvantage is the<SPANCLASS="link">more complicated syntax (<ACLASS="linkend"HREF="ch45_21.htm"TITLE="n>&m: Swap Standard Output and Standard Error ">45.21</A>)</SPAN>.Here's how to run your <EMCLASS="emphasis">cruncher</EM> program, route the <EMCLASS="emphasis">stderr</EM>through a pipe to the <EMCLASS="emphasis">mail</EM> program, and leave <EMCLASS="emphasis">stdout</EM> going to yourscreen:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>(cruncher 3>&1 1>&2 2>&3 3>&-) | mail </B></CODE><CODECLASS="replaceable"><I>yourname</I></CODE><CODECLASS="userinput"><B> &</B></CODE>12345</PRE></BLOCKQUOTE></P><PCLASS="para">To redirect <EMCLASS="emphasis">stdout</EM> to an output file and send <EMCLASS="emphasis">stderr</EM> down a pipe,try this:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>(cruncher 3>&1 ></B></CODE><CODECLASS="replaceable"><I>outputfile</I></CODE><CODECLASS="userinput"><B> 2>&3 3>&-) | mail </B></CODE><CODECLASS="replaceable"><I>yourname</I></CODE><CODECLASS="userinput"><B> &</B></CODE>12345</PRE></BLOCKQUOTE></P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">JP</SPAN></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch13_02.htm"TITLE="13.2 One Argument with a cat Isn't Enough "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 13.2 One Argument with a cat Isn't Enough "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="book"HREF="index.htm"TITLE="UNIX Power Tools"><IMGSRC="gifs/txthome.gif"SRC="gifs/txthome.gif"ALT="UNIX Power Tools"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch13_04.htm"TITLE="13.4 Problems Piping to a Pager "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 13.4 Problems Piping to a Pager "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">13.2 One Argument with a cat Isn't Enough </TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="index"HREF="index/idx_0.htm"TITLE="Book Index"><IMGSRC="gifs/index.gif"SRC="gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172">13.4 Problems Piping to a Pager </TD></TR></TABLE><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><IMGSRC="gifs/smnavbar.gif"SRC="gifs/smnavbar.gif"USEMAP="#map"BORDER="0"ALT="The UNIX CD Bookshelf Navigation"><MAPNAME="map"><AREASHAPE="RECT"COORDS="0,0,73,21"HREF="../index.htm"ALT="The UNIX CD Bookshelf"><AREASHAPE="RECT"COORDS="74,0,163,21"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="164,0,257,21"HREF="../unixnut/index.htm"ALT="UNIX in a Nutshell"><AREASHAPE="RECT"COORDS="258,0,321,21"HREF="../vi/index.htm"ALT="Learning the vi Editor"><AREASHAPE="RECT"COORDS="322,0,378,21"HREF="../sedawk/index.htm"ALT="sed & awk"><AREASHAPE="RECT"COORDS="379,0,438,21"HREF="../ksh/index.htm"ALT="Learning the Korn Shell"><AREASHAPE="RECT"COORDS="439,0,514,21"HREF="../lrnunix/index.htm"ALT="Learning the UNIX Operating System"></MAP></DIV></BODY></HTML>⌨️ 快捷键说明
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